Hello David
When it comes to QoS, IP phones are typically easy to work with because they classify and mark voice traffic by default, and their traffic can be easily identified by other network devices due to the dedicated voice VLAN they use as well as the use of CDP or LLDP to identify the devices themselves. When voice traffic originates from applications like Discord, Skype, or Cisco Webex on a computer, the classification and prioritization become less automated, but it can still be achieved using several tactics:
- Application-level marking can be performed by certain software applications (such as VoIP clients or videoconferencing software) to mark packets sent from these applications for QoS purposes.
- Application recognition/deep packet inspection can be used by network devices to classify traffic coming from particular applications. This is where NBAR can be useful, inspecting packets deeply to recognize various applications, including voice services like Skype or Webex. This inspection goes beyond basic port numbers and can identify the application-specific signatures within the traffic.
Yes, that is correct. Queuing delay is only experienced when there is congestion. All the other forms of delay mentioned occur always.
I hope this has been helpful!
Laz